This invention relates to a wood chip sorter and more particularly to a wood chip sorter of the disc screen type comprising a plurality of horizontally rotating shafts, each shaft provided with a plurality of parallel discs spaced axially therealong. The outermost peripheries of the discs of adjacent shafts interdigitate with each other, to thereby define a lateral clearance between them. The discs are commonly provided with teeth at their peripheries. In operation, the wood chips are continuously fed to one top end of the disc screen. Only those sizes of wood chips equal to or smaller than the clearance defined by the interdigitated discs should fall through the apparatus, with the remainder advanced to the outfeed end of the separator.
The prior art is aware of a variety of construction of sorters of separators of this general type, as may be seen for example by reference to U.S. Pat. Nos. 4,301,930, issued to Smith, and 4,452,694, issued to Christiansen.
While generally satisfactory for the purpose of sorting wood pulp chips, it has been observed that some larger than desired chips pass through the sorter, even with very precisely constructed components of the device. In one spacially constructed test sorter having a 2 mm spacing between the interdigitated discs, and with thin discs of less than 2 mm longitudinal thickness, wood chips of 2 mm to 5 mm were still able to pass through. This is apparently due to the teeth on the periphery of the rotating discs engaging such a relatively thick chip and forcing it, due to the resiliency of the wood, through the radial clearance between a tooth and the shaft of a next adjacent set of discs.
The relative quantity of relatively thick chips passing the specially constructed screen with thin discs was less than the quantity of relatively thick chips passing another 2 mm screen with very thick discs. This difference appeared to be a function of chip width. Study of the problem revealed that thick discs allowed a wider space between two adjacent discs on the same shaft, and thereby allowed wider chips (regardless of thickness) to reside between these adjacent discs. This provided the opportunity for the wider chip to be forced between the shaft and a disc tooth of an adjacent set of discs.